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EL84 Plate Voltage

6p14p-EB arrived

Ok,

My package arrived from deep inside the russian bunker.

I fooled around for a while trying to 'match' them up with my Hickock 6000A and then decided it was silly since my readings were not as consistent as I would have liked and my calibrated tester is under a stack of amps. (shoulder still out of whack)

First thing I noticed was they did not test as strong as 7500 like the hickock wants on a EL84. They did test a bit stronger than the US 6BQ5 I was running in my scott 222C so I stuck them in and balanced the hum. Then I tested the 6GH8A that were driving them. (Isn't that an interesting tube) and found one was well below good and the other weak.

So I checked my NOS silvanias and they tested powerful enough to lift mack trucks so in they went!

I think maybe I like the new tubes, but, without working on that bias circuit I am sure they are far from optimum.

Looked at the 222C circuits and sure enough there are some big differences between the two schematics I have, and I am pretty sure mine is not the best revision. So I will be working on that soon!

Really got to get the other tester out though. I have not found any differences between my calibrated one and my beat up one yet, but, I keep checking :)

Dan
 
Dave in CT said:
During a very recent recap, the plate voltages measured ~430v without the tuner/preamp load which would bring it in around 400v (perhaps a little less) when back in the console. Does anyone have experience running EL84s at this high a plate voltage?
Click to expand...

I built a Dynaco ST35 clone, but used the "wrong" power transformer. My plate voltages ended up around 405 VDC. This is a cathode biased amp, so subtract 15 volts or so to determine what is actually across the tube.

I've used lots of 70's and 80's vintage Reflektor 6p14p variants. I tried the vanilla kind, the -K kind, and the long life -EB kind. For the most part, I've just had the plain 6p14p (no suffix) tubes in and they have shown no signs of stress. The cathode resistors are adjusted to keep the idle current around 30~32 mA per tube. I've never seen red plates or glowing screens in this amp. I ran it nightly for almost a year without trouble. I'd still be using it now, but I'm spending more time with other amps.

 
Those Soviet Military tubes get my vote. I have several. I also have several GE 7189A tubes and prefer to save them and use the Soviet Military. They work just fine.

Think about it... If they did not last and measure up, someone would most likely be sent to the Gulag. Can't speak to modern manufacturing but I am pleased with those mid 80s tubes.

Just my 2¢...
 
This is all very interesting and puzzling at the same time. My recent GE console has 2 Realistic 7189A tubes and that is what is called for on the schematic. I thought the replacements were the Sovtek el84M tubes and would work fine. No? I did test it with a pair of old 6bq5 tubes and all was fine, but I am now continuing with what it came with, the 7189A. What do I do when I need replacements? John
 
I think that the 7189/EL84/6BQ5 pin-out is all the same. Where the confusion enters is the "A" suffix; 7189A...
 
I like it!

I like that amp,

Even the 2x4 presentation does not take away from how nicely you did all the work on the electronics. A real beauty.

Any idea what the -k means?

I bought 20 of the -eb variety because I want to have enough to never worry about it again on this amp. (plus I have several guitar amps that use them)
 
what I heard

sloober said:
This is all very interesting and puzzling at the same time. My recent GE console has 2 Realistic 7189A tubes and that is what is called for on the schematic. I thought the replacements were the Sovtek el84M tubes and would work fine. No? I did test it with a pair of old 6bq5 tubes and all was fine, but I am now continuing with what it came with, the 7189A. What do I do when I need replacements? John
Click to expand...

I am strongly suspicioned that your amp must be set up correctly for the 6bq5/el84m tubes as far as pin out goes

1, 6 , and 8 should be unconnected to the internals of the tube on the 6bq5/7189 - but they are connected internall for reasons known only to a guy with a slide rule and horned rimmed glasses on the 7189A

http://www.mif.pg.gda.pl/homepages/frank/sheets/106/7/7189.pdf <-- this link shows the two pin outs right next to each other.

Don't pay any attention to my half baked attempts to explain it, rather, look at the pin outs and you will probably know so much more than I ever even thought of.

Man, I want to start biasing this amp but I will set my shoulder back if I lift it up much, I will go test the preamp tubes instead. :banana:

Dan
 
Looks like I can use the EL84M without worry. Looking at the schematic and traces on the PCB of my amp, Pins 1-6-8 are all going nowhere. Plate voltage as specified on the schematic is 305V. Thanks for the info. John
 

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305!

305!!

Lucky dog.

Mine is a tubelab experiment. . . . just kidding, but it is way over 400 - OHHH, I have the EL84M type in it now, I can stick the correct rectifier in it now and crank the voltage up a little.

(Going to turn off the lights and check it out after a few min)

Dan
 
ok Stuck the 5AR4 into the scott 222c

Man,

I miss my Scott 222c thread.

Ok, so I stuck the 5AR4 in place of the 5U4GB since I now had the EL84M style tubes in to replace the weak 6BQ5 USA tubes.

(I was trying to keep the plate voltage as low as possible since I was not going to bias them properly for the higher than spec voltages the 7189 design provided)

Here are the voltages I saw on the tubes in this order: Original parts and 5U4GB -> 5AR4 with a lot of new parts installed, then back to the 5U4GB

Pin#

2) -15.6 --> -18 --> -18.44
3) 1.6 mv --> 1.5mv --> .6mv
7) 385 --> 424 --> 401
9) 327 --> 360 --> 343

So I am back to the middle voltages.

First thing I notice is the Bass cranks back up where I like it!

Oh, I also used some of those nasty chinese high gain 12AX7 tubes with the chrome looking strips inside the tubes like Mikey Soldano likes. They are driving the stew out of my amp.

It actually sounds pretty good. I am testing all my 7025 tubes now to see what I find that might be a touch more mellow until I can get some LPS tubes into whatever socket I am actually using for my extra inputs.

Dan
 
Great site~

Ty_Bower said:
Thank you. I'm pleased with the way it turned out. Some day I need to put some Watkin's Danish oil on it. The -K means "special audio, vibration proof". I can't tell any difference, but I think it's neat they are nearly 35 years old. There's a good reference on all the Russian numbering schemes here:

http://www.jogis-roehrenbude.de/Russian/russ_roehre_rue_dat.pdf
Click to expand...


Thanks for the site. I looked at it and thought, well he told me what the k means so that is all I need,

But the site is really pretty interesting

Dan
 
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